Devices, systems, and methods for mapping organ profiles

ABSTRACT

Devices, systems, and methods for the localization of body lumen junctions and other intraluminal structure are disclosed. Various embodiments permit clinicians to identify and locate lesions and/or anatomical structures within a lumen and accurately place leads and/or devices within a lumen, through determining the intralumen conductance and/or cross-sectional area at a plurality of locations within the body lumen.

PRIORITY

This International Patent Application: (1) claims priority to U.S.Provisional Patent Application Ser. No. 60/881,840, filed Jan. 23, 2007,which is hereby incorporated by reference in its entirety into thisdisclosure; and (2) claims priority to International Application No.PCT/US2007/015239, filed Jun. 29, 2007, which (a) claims priority toU.S. Provisional Patent Application Ser. No. 60/817,422, filed Jun. 30,2006; (b) claims priority to and is a continuation-in-part of U.S.patent application Ser. No. 10/782,149, filed Feb. 19, 2004, whichclaims priority to U.S. Provisional Patent Application Ser. No.60/449,266, filed Feb. 21, 2003, U.S. Provisional Patent ApplicationSer. No. 60/493,145, filed Aug. 7, 2003, and U.S. Provisional PatentApplication Ser. No. 60/502,139, filed Sep. 11, 2003; and (c) claimspriority to and is a continuation-in-part of U.S. patent applicationSer. No. 11/063,836, filed Feb. 23, 2005, which claims priority to U.S.patent application Ser. No. 10/782,149, filed Feb. 19, 2004. Thecontents of each of these applications are hereby incorporated byreference in their entirety into this disclosure.

BACKGROUND

Treatment of certain cardiovascular diseases such as aortic aneurysms orchronic heart failure often includes positioning devices within theaorta or the coronary sinus through catheterization. Such proceduresrequire precise placement of the implanted devices within the targetlumens, and can result in severe complications if such implantations areinaccurate. Accordingly, having a clear map of the aorta and/or coronarysinus minimizes the risks involved in these procedures.

An aortic aneurysm is a ballooning of the wall of an artery resultingfrom the weakening of the artery due to disease, heredity, aging orother conditions. When an area of the aortic wall weakens, the pressureof the blood flowing through the weakened area causes the vessel wall toballoon out, forming a blood-filled aneurysm sack. Although mostaneurysms are initially small, aneurysms tend to enlarge over time. Leftuntreated, the aneurysm will frequently rupture, resulting in loss ofblood through the rupture.

Aortic aneurysms are the most common form of arterial aneurysm and arelife threatening due to the massive internal bleeding that results fromrupture. In the past 30 years, the occurrence of abdominal aorticaneurysms (“AAA”), in particular, has increased threefold. According tothe Society of Vascular Surgeons, ruptured aneurysms account for morethan 15,000 American deaths each year, making the AAA the thirteenthleading cause of death in the United States.

The aorta is the main artery that carries blood from the heart to therest of the body. The aorta arises from the left ventricle of the heart,extending upward and bending over behind the heart, and thereafterextending downward through the thorax and abdomen. The abdominal aortasupplies the two side vessels to the kidneys, the renal arteries. Belowthe level of the renal arteries, the abdominal aorta continues to aboutthe level of the fourth lumbar vertebrae where it divides into the iliacarteries. The iliac arteries supply blood to the lower extremities andperineal region. Accordingly, the aorta is a major arterial component ofthe circulatory system and maintaining its general condition is criticalto the overall health of the patient.

AAA is the most common type of aortic aneurysm. Specifically, AAA is ananeurysm that occurs in the portion of the abdominal aorta that isparticularly susceptible to weakening between the renal arteries and theiliac arteries. While, in other areas of the aorta the indication thatintervention is necessary is when the aneurysm reaches about 5 cm indiameter, an aortic aneurysm larger than about 4 cm in diameter in thissection of the aorta is ominous. Left untreated, the AAA may rupture,resulting in rapid and usually fatal hemorrhaging.

Although the mortality rate for an aortic aneurysm is extremely high(about 75-80%), there is also considerable mortality and morbidityassociated with surgical intervention to repair an aortic aneurysm. Thisintervention typically involves going through the abdominal wall to thelocation of the aneurysm in order to bypass or replace the diseasedsection of the aorta. A prosthetic device, typically a synthetic tube,is often used for this purpose. The graft serves to exclude the aneurysmfrom the circulatory system, thus relieving the pressure and stress onthe weakened section of the aorta at the aneurysm.

Repair of an aortic aneurysm by surgical means is a major operativeprocedure. In addition, substantial morbidity accompanies the procedure,resulting in a protracted recovery period. Finally, the procedureentails a substantial risk of mortality. While surgical intervention maybe required in spite of these risks, certain patients may not be able totolerate the stress of intra-abdominal surgery. It is desirable toreduce the mortality and morbidity associated with intra-abdominalsurgical intervention.

In recent years, methods have been developed to attempt to treat anaortic aneurysm without the attendant risks of surgical intervention.One such minimally invasive alternative is endovascular aneurysm repair(“EVAR”). EVAR treatment involves the placement of an endovascular stentin the aneurismal area of the aorta through a percutaneous technique.Specifically, in most circumstances, the endovascular stent is insertedinto a blood vessel (artery or vein), usually through an entry sitelocated in the upper leg or neck. Under fluoroscopy, the stent isnavigated through the blood vessels until it reaches the aorta where itis positioned over the aneurysm.

While EVAR has been reported to have a lower mortality rate as comparedto open surgical repair, to effectuate a successful delivery of EVAR, itis necessary to have a clear map of the aorta such that the stent can beproperly positioned. Although the aneurysmic regions of the aorta may bequite diseased and atherosclerotic, for the procedure to be successful ahealthy portion of the aorta must be present to serve as a landing zonefor the stent. For example, securing the stent to a diseased region ofthe aorta will result in a faulty seal that will not adequately reroutethe blood flow away from the aneurysmic region, thereby resulting in areoccurrence of the condition. As accurate placement of the stent iscritical, visualization of the aortic structure has been an obstacle forproper navigation during delivery of the stent. Currently, cliniciansperform magnetic resonance imaging prior to delivering the stent inorder to supply an axial profile of the aorta. However, magneticresonance imaging is expensive and time consuming to obtain, and theresults exhibit limited spatial resolution.

Chronic heart failure (“CHF”) is another cardiovascular disease, thetreatment of which often includes catheterization. CHF is a diseasecondition in which the heart fails to function efficiently as a pump andcannot provide sufficient blood flow and/or pressure to satisfy thenormal circulatory needs of a patient. A patient with acute CHF oftenexperiences sudden shortness of breath, fainting, and irregular heartbeats that require frequent emergency room treatments. In its chronicform, CHF leads to repeated hospital stays, a deterioration in qualityof life, and significant costs to the healthcare system.

In about 30% of CHF patients, the disease process compromises themyocardium's ability to contract, which thereby alters the conductionpathways through the heart. A healthy heart has specialized conductionpathways in both the atria and the ventricles that enable the rapidconduction of excitation (i.e. depolarization) throughout themyocardium. Normally, the sinoatrial node (“SA node”) initiates eachheart-beat cycle by depolarizing so as to generate an action potential.This action potential propagates relatively quickly through the atria,which react by contracting, and then relatively slowly through theatrio-ventricular node (“AV node”). From the AV node, activationpropagates rapidly through the His-Purkinje system to the ventricles,which also react by contracting. This natural propagation synchronizesthe contractions of the muscle fibers of each chamber and synchronizesthe contraction of each atrium or ventricle with the contralateralatrium or ventricle.

When a patient exhibits damage to the electrical system of the heart, asis often seen in patients with CHF, severe issues may arise. Disruptionof the conductance pathways through the heart can cause a delay in thebeginning of right or left ventricular systole and thereby induceasynchronous atrial and ventricular activation.Electrocardiographically, this dysynchrony is manifested as a long QRSinterval. Alterations in ventricular contractility frequently compromisethe ability of the failing heart to eject blood and may consequentlyincrease the severity of the regurgitant flow through the mitral valve.In patients exhibiting these severe symptoms, the intraventricularconduction delays lead to clinical instability associated with a greatlyincreased risk of death.

Since 2001, approximately 271,000 heart failure patients in the UnitedStates have received cardiac resynchronization therapy (“CRT”) to treatmoderate to severe heart failure (“HF”). Conventional CRT methods employa pacemaker to pace both ventricles of the heart such that the heart canresynchronize. CRT devices have three leads; the first positioned in theatrium, the second positioned in the right ventricle, and the thirdinserted through the coronary sinus to pace the left ventricle.

Due to the required placement of the third lead, the implantation andmaintenance of a CRT device are associated with a greater risk than theimplantation and maintenance of a standard pacemaker device. Primarily,it is a difficult procedure to advance the pacing lead into the coronarysinus and cardiac veins and, thus, implantation fails in approximately8% of patients. Further, in approximately 6% of patients, implantationis compromised by dissection or perforation of the coronary sinus orcardiac vein. Severe complications are associated with the inaccurateimplantation of a pacing lead, including complete heart block,hemopericardium, and cardiac arrest (which, together, occurred in about1.2% of patients).

As accurate placement of the leads is critical, the ability to visualizea map or profile of the coronary sinus is important to ensure propernavigation. Conventionally, clinicians use cardiac angiography tovisualize the lumen of the blood vessels and the heart chambers. Cardiacangiography typically involves using a combination of injections ofradiocontrast agent or dye and x-ray fluoroscopy to visualize theposition and size of blood within the heart. This process, however, isnot particularly accurate and does not provide a detailed profile of thecoronary sinus.

Thus, there is a need for an efficient, accurate, easy to use, andreasonably priced technique for determining the longitudinal profile ofthe aorta and the coronary sinus.

BRIEF SUMMARY

Various embodiments of devices, systems, and methods for localizationof, body lumen junctures are disclosed herein. At least some of thedisclosed embodiments allow a clinician to identify desired anatomicalstructures with a higher spatial resolution than with conventionaltechniques. For example, in certain embodiments, a clinician may useembodiments of the devices, systems and methods disclosed herein toaccurately identify various bifurcations branching off of the coronarysinus. A clinician may further use the embodiments described herein toaccurately place a lead within a coronary sinus or a bifurcationbranching therefrom. In certain other embodiments, a clinician may useembodiments of the devices, systems and methods disclosed herein tocreate a conductance profile of an aorta that is capable of showing thelocations of lesions or other structures. In this manner, conductanceprofile can be used to accurately treat an aortic aneurysm by employinga stent.

Some embodiments disclosed herein include systems for localizing a bodylumen junction or other intraluminal structure. These systems comprise acatheter having a proximal end and a distal end for placement into abody lumen. The catheter may comprise a first electrode and a secondelectrode, and each of the first and second electrodes have a proximalend and a distal end; the distal ends of the first and second electrodesare located between the proximal and distal ends of the catheter. Insome embodiments, the catheter may comprise a thin wire. The systemfurther comprises a processor connected to the first and secondelectrodes of the catheter. The processor is capable of collectingconductance data to determine a profile of the body lumen. Theconductance data is collected at a plurality of locations within thebody lumen and determined at each of the plurality of locations when thedistal ends of the first and second electrodes are immersed in a fluidwithin the body lumen. In some embodiments, the processor is alsocapable of calculating a cross-sectional area of the body lumen at eachof the plurality of locations within the body lumen using theconductance data.

For certain embodiments of such systems, the relevant body lumencomprises at least a portion of an atrium, coronary sinus, aorta, apulmonary vein-atrial junction, a blood vessel, a biliary tract, or anesophagus. Indeed, many embodiments may be used in connection with anyother body lumen that is suitable for access and localization.

The body lumen may have at least some fluid inside, and the fluid maycomprise blood or another suitable fluid, such as a solution of NaClhaving a known conductivity. Certain embodiments of the catheter have apassageway for passing fluid through the catheter to the location of thedistal ends of the first and second electrodes, such that the fluidpassing through the passageway comes in contact with the distal ends ofthe first and second electrodes. For some embodiments, the conductancedata is determined at each of a plurality of locations within the lumenwhen the distal ends of the first and second electrodes are immersed ina first fluid having a first conductivity and then a second fluid havinga second conductivity. The conductance data may comprise a firstconductance value determined at each of the plurality of locations whenthe distal ends of the first and second electrodes are immersed in thefirst fluid and a second conductance value determined at each of theplurality of locations when the distal ends of the first and secondelectrodes are immersed in the second fluid. The profile of the bodylumen is therefore determined from the first and second conductancevalues collected from each of the plurality of locations, the firstconductivity of the first fluid, and the second conductivity of thesecond fluid. The profile may consist of actual or relative values forcross-sectional areas or conductances.

Many embodiments disclosed herein have a catheter with at least fourelectrodes, including at least two excitation electrodes and at leasttwo detection electrodes. Further, in certain embodiments, the cathetermay comprise a thin wire having at least four electrodes. Each of theelectrodes has a proximal end and a distal end, wherein the proximalends of the electrodes may be connected to the processor directly orindirectly. In at least some embodiments, the distal ends of theexcitation electrodes are located between the proximal and distal endsof the catheter, and the distal ends of the detection electrodes arelocated between the distal ends of the excitation electrodes.

Certain embodiments disclosed herein include a number of steps forlocalizing a junction or other structure within a body lumen, includingproviding an embodiment of a system as disclosed herein; introducing thecatheter into the body lumen; providing electrical current flow to thebody lumen through the catheter; measuring a first conductance value ata first location in the body lumen; moving the catheter to a secondlocation in the body lumen; measuring a second conductance value at asecond location in the body lumen; and determining a profile of the bodylumen based on the first conductance value of the first location and thesecond conductance value of the second location. The profile of the bodylumen resulting from such embodiments may include relative conductancesand/or relative cross-sectional areas.

For other embodiments, the actual values for the lumen conductance orcross-sectional area are determined by further injecting a known volumeof a first solution having a first conductivity into the body lumen;injecting a second solution having a second conductivity into the bodylumen, wherein the second solution has a second volume and wherein thesecond conductivity does not equal the first conductivity; measuring asecond conductance value at the first location in the body lumen;calculating the conductance at the first location in the body lumen;measuring a first conductance value at a second location in the bodylumen; and calculating the conductance at the second location in thebody lumen. The determination of the profile of the body lumen may bebased on the conductance of the first location, the conductance of thesecond location, and the conductivities of the first and secondsolutions. In addition, in some embodiments, the tissue is ablated afterlocalization using the same catheter for both aspects of the procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the visual output of an embodiment of a catheter system forlocalization during an experiment of movement through an interior of asurgical glove;

FIG. 2A shows the visual output of an embodiment of a catheter systemfor localization during an experiment of movement through an interior ofa heart;

FIG. 2B shows a mean lumen profile of an aorta as generated by oneembodiment of a catheter system for localization;

FIG. 2C shows a mean lumen profile of an aorta generated by oneembodiment of a catheter system for localization and further comprisingcorrections for bifurcations;

FIG. 3A shows an embodiment of a catheter for localization of a bodylumen juncture;

FIG. 3B shows another embodiment of a catheter for localization of abody lumen juncture;

FIG. 3C shows an embodiment of a catheter for localization and ablationof a body lumen juncture;

FIG. 4A shows another embodiment of a catheter for localization;

FIG. 4B shows an embodiment of a balloon catheter having impedancemeasuring electrodes supported in front of the stenting balloon;

FIG. 4C shows another embodiment of a balloon catheter having impedancemeasuring electrodes within and in front of the balloon;

FIG. 4D shows an embodiment of a catheter having an ultrasoundtransducer within and in front of the balloon;

FIG. 4E shows an embodiment of a guide catheter with wire and impedanceelectrodes;

FIG. 4F shows an embodiment of a catheter with multiple detectionelectrodes;

FIG. 5A shows an embodiment of a catheter in cross-section proximal tothe location of the sensors showing the leads embedded in the materialof the probe;

FIG. 5B shows another embodiment of a catheter in cross-section proximalto the location of the sensors showing the leads run in separate lumens;

FIG. 6 is a schematic of an embodiment of a system showing a cathetercarrying impedance measuring electrodes connected to a data processorequipment and excitation unit for the measurement of conductance and/orcross-sectional area;

FIG. 7A shows the detected filtered voltage drop as measured in theblood stream before and after injection of 1.5% NaCl solution;

FIG. 7B shows the peak-to-peak envelope of the detected voltage shown inFIG. 7A;

FIG. 8A shows the detected filtered voltage drop as measured in theblood stream before and after injection of 0.5% NaCl solution;

FIG. 8B shows the peak-to-peak envelope of the detected voltage shown inFIG. 8A;

FIG. 9 shows one embodiment of a catheter for localization being used inthe treatment of an aortic aneurysm;

FIG. 10 shows one embodiment of a treatment for an aortic aneurysm;

FIG. 11A shows the voltage recorded by a conductance catheter with aradius of 0.55 mm for various size vessels (vessel radii of 3.1, 2.7,2.3, 1.9, 1.5 and 0.55 mm for the six curves, respectively) when a 0.5%NaCl bolus is injected into the treatment site; and

FIG. 11B shows the voltage recorded by a conductance catheter with aradius of 0.55 mm for various size vessels (vessel radii of 3.1, 2.7,2.3, 1.9, 1.5 and 0.55 mm for the six curves, respectively) when a 1.5%NaCl bolus is injected into the treatment site.

DETAILED DESCRIPTION

It will be appreciated by those of skill in the art that the followingdetailed description of the disclosed embodiments is merely exemplary innature and is not intended to limit the scope of the appended claims.

During various medical procedures involving intraluminal insertion ofcatheters or other devices, proper navigation of the device through bodylumens, such as blood vessels or the heart, is critical to the successof the procedure. This is especially true with respect tocatheterization of the aorta and coronary sinus. Indeed, unless thetissue targeted for treatment or diagnosis is properly located, theprocedure can be ineffective or, even worse, damaging. For example, withrespect to treatment of an aortic aneurysm, a stent must be delivered toa disease-free landing zone adjacent to the aneurysm. In the event thestent is inaccurately placed—due to disorientation within the lumen orotherwise—a sufficient seal will not be achieved and the treatment willbe ineffective.

Similarly, in the treatment of ventricular fibrillation using CRTtherapy, an electrical lead must be placed precisely within the coronarysinus through the ostium of the coronary sinus (the junction of thecoronary sinus and the right atrium). Achieving the proper placement isan exceptionally difficult procedure, in part because there are variousanatomical structures located within the right atrium that can be easilyconfused with the coronary sinus (e.g., the fossa ovalis, the custaclanridge, etc.). These particular features of the heart do not show up wellon a fluoroscope, therefore making the procedure quite difficult andtime consuming for the clinician. Nevertheless, the clinician must beable to accurately insert the catheter into the coronary sinus withoutperforating the vessel or causing any trauma to the adjacent structures,all while the heart is beating. Having a clear map of the coronary sinusin the form of a lumen profile minimizes the risks involved with thisprocedure and drastically reduces the risk of damaging the surroundingstructures. Accordingly, a number of the embodiments disclosed hereinpermit a clinician to readily locate a catheter, or other medicaldevice, within a body lumen in relation to body lumen junctions or otheranatomical structures within the lumen.

In addition to being able to properly navigate body lumens, it is alsobeneficial to obtain accurate measurements of the luminalcross-sectional area in a targeted location as this enables accurate andscientific stent sizing and placement. Obtaining such accuratemeasurements can improve clinical outcomes by avoiding under or overdeployment and under or over sizing of a stent which can cause acuteclosure or in-stent restenosis. At least one embodiment disclosed hereinallows a clinician to accurately measure the luminal cross-sectionalarea of an organ or body lumen. This leads to proper localization of atargeted tissue, accurate stent sizing and placement, and increasedfavorable outcomes for certain medical procedures.

In at least one embodiment, electrical conductance is measured withinthe body lumen and a profile of relative conductance values isdisplayed, while other embodiments use conductance data to calculateluminal cross-sectional areas and display a profile of relativecross-sectional areas along a portion of the lumen. These profilesenable the clinician to readily locate the targeted tissue for furthertreatment, such as for placement of a lead or stent.

Many of the disclosed embodiments do not calculate an absolute value fora lumen's cross-sectional area, but instead measure electricalconductance through a portion of the lumen to form a profile of thelumen. Often, the profile comprises relative conductances taken alongthe lumen. However, because conductance is proportional tocross-sectional area, as explained herein, the profile can compriserelative cross-sectional areas that have been determined from theconductances taken along the lumen.

By monitoring this profile during catheterization, the clinician canvisualize the anatomical structure of the lumen. For example, using apush through or a pull back of a disclosed embodiment of a catheterthrough a lumen, a clinician is able to localize a junction or otherarchitectural marker in the body lumen. Such a push through or pull backtechnique will reflect, in relative terms, the lumen's changes inconductance, and therefore its changes in cross-sectional area, as thecatheter moves, thereby depicting changes in lumen structure across adistance. Based on such changes in lumen structure, a clinician candetermine the locations of various anatomical markers of the lumen, aswell as the location of the catheter in relation to those markers.

In one example, localization of the junction between an aortic aneurysmand the healthy aortic wall is achieved by assessing the change inconductance (and therefore in cross-sectional area) of the lumen as thecatheter is pulled through the aorta and passes the affected tissue.Once a specific lumen junction or other anatomical structure islocalized, the clinician can better treat a targeted tissue at or nearthat identifying structure. Such treatment may include, for example andwithout limitation, angioplasty or stent delivery. Further, becauseclinicians can accurately visualize the anatomic structure of the lumen,a catheter may be inserted into even the smallest blood vessel with ahigh degree of accuracy (e.g., the coronary sinus).

Experiments have demonstrated the ability of the disclosed embodimentsto provide accurate and reliable feedback as to the location of acatheter within a body lumen. For instance, a surgical glove was filledwith saline to simulate a left atrium (the palm) and pulmonary veins(the fingers). A catheter configured for localization as describedherein was pulled back from inside a finger to the palm, therebysimulating the transition from a pulmonary vein to the atrium. FIG. 1shows the conductance profile 10 as the catheter was pulled back from afinger into the palm of the glove, then was pushed into a finger. As canbe seen, the profile shows that the conductance of the palm wassignificantly larger than the conductance of the finger, and thetransition or demarcation from the finger to the palm is apparent.Because conductance and cross-sectional area (“CSA”) are proportional(as discussed below), conductance profile 10 is proportional to the CSAprofile (not shown) and distinguishes between the smallercross-sectional area of the fingers and the larger cross-sectional areaof the palm.

A similar pullback experiment was carried out in a heart. Starting fromthe pulmonary vein, a catheter configured for localization as describedherein was pulled back from the pulmonary vein into the left atrium andventricle. FIG. 2 shows a conductance tracing 12 that reflects theconductance for each region of the body lumen as the catheter is pulledback over a distance of about 5 cm from a starting point in thepulmonary vein. The pulmonary vein can be clearly identified byreference to its relative conductance compared to those of the leftatrium, the mitral valve, and the left ventricle. Indeed, the atrial CSAis significantly larger than that of the pulmonary vein, and the atrialCSA increases with distance away from the pulmonary vein-atrialjunction. A reduction in CSA is then observed as the catheter approachesand crosses the mitral valve. Once the catheter progresses through themitral valve into the ventricle, the CSA increases gradually.

Using conductance data like that shown in FIG. 2, a clinician canprecisely obtain his or her orientation within the aorta, and therebylocalize an aortic aneurysm. For example, the various points ofbifurcation of the aorta can be identified using the type of conductancedata shown in FIG. 2A. Specifically, in FIG. 2A, where the conductancedata begins to increase, the data indicates that the luminal CSA hasincreased, especially when such an increase is drastic.

A conductance or impedance catheter measures conductance within a bodylumen using a number of electrodes. Referring now to FIG. 3A, there isshown a conductance catheter 400 configured to localize a body lumenjunction using conductance measurements. Catheter 400 has a proximal end405 and a distal end 410, which is suitable for introduction into a bodylumen. In one embodiment, catheter 400 comprises a thin conductance wirethat is capable of accessing the coronary sinus. In addition, catheter400 includes a pair of excitation electrodes 415 and a pair of detectionelectrodes 420. Each of excitation electrodes 415 and detectionelectrodes 420 has a proximal end that is capable of attachment to aprocessing system (not shown) and a distal end that is located oncatheter 400 between proximal end 405 and distal end 410. The distalends of detection electrodes 420 are located on catheter 400 between thedistal ends of excitation electrodes 415. Excitation electrodes 415 areconfigured to emit a measured electrical charge into the body lumen,while detection electrodes 420 detect the amount of the charge thattravels through a fluid within the body lumen. As explained in moredetail below, a processing system calculates the change in electricalcharge to determine the conductance through the lumen at any givenlocation in the lumen.

As shown in FIG. 3A, electrodes 415 and 420 are located at distal end410 of catheter 400. However, the positioning of the electrodes is notlimited to this distal end portion, but may be anywhere on the catheterthat can assist in providing conductance information to the clinician.Furthermore, multiple sets of electrodes (see FIG. 4F) may also be usedto provide additional information used for mapping the interioranatomical structure of an internal organ, vessel, or other body lumen.

A number of embodiments disclosed herein, such as the embodiment shownin FIG. 3A, have at least two detection electrodes and two excitationelectrodes. However, in the embodiment shown in FIG. 3B, only twoelectrodes are used. Catheter 425 has a proximal end 430 and a distalend 435, as well as a first electrode 440 and a second electrode 445.Each of electrodes 440 and 445 has a proximal end (not shown) and adistal end located on catheter 425 between proximal end 430 and distalend 435. Because catheter 425 has only two electrodes, each electrodemust serve both the excitation function and the detection function. Toenable a single electrode to send and measure the electrical charge, adelay must be added to the circuit. Additionally, a bipolar cathetermust be stationary at the time of measurement, requiring the clinicianto obtain a profile by moving the catheter to a desired location,stopping and taking a measurement, and then moving the catheter again.By contrast, tetrapolar catheters may take a continuous conductancemeasurement as the catheter is pulled or pushed through the body lumen,thereby giving a more detailed profile as compared to bipolar catheters.

Although at least some embodiments can properly measure lumenconductance in the presence of a bodily fluid (such as blood) within thelumen, certain other embodiments may use fluids injected into the bodylumen to properly calculate lumen conductance and/or cross-sectionalarea, as explained herein. Therefore, some embodiments include a channelthrough which fluid is injected into the body lumen. In the embodimentshown in FIG. 3C, infusion passageway 490 is configured to permit suchinjection so that fluid flowing from passageway 490 will flow at leastto the location of the distal ends of excitation electrodes 470 anddetection electrodes 480. Thus, the fluid passing through passageway 490into the lumen will come in contact with the distal ends of excitationelectrodes 470 and detection electrodes 480.

Referring now to FIGS. 4A to 4F, several embodiments of catheters areillustrated. With reference to the embodiment shown in FIG. 4A, there isshown an impedance catheter 22 with four electrodes 25, 26, 27, and 28placed close to distal end 19 of the catheter. Electrodes 25 and 27 areexcitation electrodes, while electrodes 26 and 28 are detectionelectrodes, thereby permitting measurement of conductance (and thereforecalculation of cross-sectional area) during advancement of the catheter,as described in further detail below.

In addition, catheter 22 possesses an optional infusion passageway 35located proximal to excitation electrode 25, as well as optional ports36 for suction of contents of the body lumen or for infusion of fluid.The fluid to inject through passageway 35 or ports 36 can be anybiologically compatible fluid, but, for some circumstances disclosedherein, the conductivity of the fluid is selected to be different fromthat of blood.

In various embodiments, including for example the embodiment shown inFIG. 4A, the catheter contains a channel 31 for insertion of a guidewire to stiffen the flexible catheter during insertion or datarecording. Additionally, channel 31 may be used to inject fluidsolutions of various concentrations (and various conductivities) intothe body lumen of interest. An additional channel 32 may be connected tothe catheter such that the electrical wires connected to the one or moreelectrodes on the catheter are directed through channel 32 and to a dataprocessor, such as data processor system 100 (see FIG. 6), through anadaptor interface 33, such as an impedance module plug or the like, asdescribed in more detail below.

In addition to localization, some embodiments disclosed herein provideother functionality. FIGS. 4B-4F show a number of embodiments ofconductance catheters having various functions. For example, severalsuch embodiments include an angioplasty balloon, in addition toimpedance electrodes (see, e.g., FIG. 4B). Such catheters may includeelectrodes for accurate detection of organ luminal cross-sectional areaand ports for pressure gradient measurements. Hence, when using suchcatheters, it is not necessary to change catheters during the procedure,as with the current use of intravascular ultrasound. In at least oneembodiment, the catheter can provide direct measurement of thenon-stenosed area of the lumen, thereby allowing the selection of anappropriately sized stent for implantation.

With reference to the embodiment shown in FIG. 4B, four wires arethreaded through one of the two lumens of catheter 20 (a 4 Fr.catheter). Catheter 20 has a proximal end and a distal end 19, as wellas excitation electrodes 25, 27 and detection electrodes 26, 28 placedat or near distal end 19. Proximal to these electrodes is an angioplastyor stenting balloon 30 capable of being used to treat stenosis. Thedistance between the balloon and the electrodes is usually small, in the0.5 mm to 2 cm range, but can be closer or farther away, depending onthe particular application or treatment involved. The portion ofcatheter 20 within balloon 30 includes an infusion passageway 35 and apressure port 36.

Detection electrodes 26 and 28 are spaced 1 mm apart, while excitationelectrodes 25 and 27 are spaced 4 mm to 5 mm from either side of thedetection electrodes. The excitation and detection electrodes typicallysurround the catheter as ring electrodes, but they may also be pointelectrodes or have other suitable configurations. These electrodes maybe made of any conductive material, such as platinum iridium or amaterial with a carbon-coated surface to avoid fibrin deposits. In atleast one embodiment, the detection electrodes are spaced with 0.5 mm to1 mm between them and with a distance of between 4 mm and 7 mm to theexcitation electrodes on small catheters. On large catheters, for use inlarger vessels and other larger body lumens, the electrode distances maybe larger. The dimensions of the catheter selected for a treatmentdepend on the size of the vessel or other body lumen and are preferablydetermined in part on the results of finite element analysis.

In one approach, dimensions of a catheter to be used for any givenapplication depend on the optimization of the potential field usingfinite element analysis described below. For small organs or inpediatric patients, the diameter of the catheter may be as small as 0.3mm. In large organs, the diameter may be significantly larger dependingon the results of the optimization based on finite element analysis. Theballoon will typically be sized according to the preferred dimension ofthe organ after the distension. The balloon may be made of materialssuitable for the function, such as, for example, polyethylene, latex,polyestherurethane, or combinations thereof. In at least one embodiment,the balloon comprises a thickness of a few microns. The catheter maycomprise PVC or polyethylene material, although other materials may beused equally well. The tip of the catheter can be straight, curved, orangled to facilitate insertion into the coronary arteries or other bodylumens, such as, for example, the biliary tract.

Referring again to FIG. 4B, catheter 20 may also include severalminiature pressure transducers (not shown) carried by the catheter orpressure ports for determining the pressure gradient proximal to thesite where the conductance is measured. The pressure is preferablymeasured inside the balloon and proximal to, distal to, and at thelocation of the conductance measurement, and locations proximal anddistal thereto, thereby enabling the measurement of pressure recordingsat the site of stenosis and also the measurement of pressure-differencealong or near the stenosis. In one embodiment, shown in FIG. 4B,catheter 20 includes pressure port 90 and pressure port 91 proximal toor at the site of the conductance measurement for evaluation of pressuregradients. As described below with reference to FIGS. 5A, 5B, and 6, inat least one embodiment, the pressure ports are connected by respectiveconduits in catheter 20 to pressure sensors in the data processor system100 (see FIG. 6). Such pressure sensors are well known in the art andinclude, for example, fiber-optic systems, miniature strain gauges, andperfused low-compliance manometry.

In at least one embodiment, a fluid-filled silastic pressure-monitoringcatheter is connected to a pressure transducer. Luminal pressure can bemonitored by a low compliance external pressure transducer coupled tothe infusion channel of the catheter. Pressure transducer calibrationwas carried out by applying 0 and 100 mmHg of pressure by means of ahydrostatic column.

In another embodiment, shown in FIG. 4C, a catheter 39 includes anotherset of excitation electrodes 40, 41 and detection electrodes 42, 43located inside the angioplastic or stenting balloon 30 for accuratedetermination of the balloon cross-sectional area during angioplasty orstent deployment. These electrodes are in addition to electrodes 25, 26,27, and 28.

In various embodiments, the conductance may be measured using atwo-electrode system (see FIG. 4D). In other embodiments, such asillustrated in FIG. 4F, the conductances at several locations can bemeasured at the same time using an array of five or more electrodes.Here, excitation electrodes 51, 52 are used to generate the currentwhile detection electrodes 53, 54, 55, 56, and 57 are used to detect thecurrent at their respective sites.

In another embodiment, shown in FIG. 4D, catheter 21 has one or moreimaging or recording devices, such as, for example, ultrasoundtransducers 50 for cross-sectional area and wall thickness measurements.As shown, transducers 50 are located near distal end 19 of catheter 21.

With reference to the embodiment shown in FIG. 4E, electrodes 25, 26,27, and 28 are built onto a wire 18, such as, for example, a pressurewire, and inserted through a guide catheter 23, where the infusion of abolus can be made through the lumen of the guide catheter. Adaptorinterface 33 may be used to house and guide the electrical wires(including proximal portions of the excitation and detection electrodes)to a data processor system 100, while a side channel 34 is used toinject various fluids into catheter 23. In yet another embodiment (notillustrated), the catheter includes a sensor for measurement of the flowof fluid in the body lumen.

Many of the embodiments described herein may be used as part of asystem, which includes suitable connections between the system's variousparts. As described below with reference to FIGS. 5A, 5B, and 6, theexcitation and detection electrodes are electrically connected toelectrically conductive leads in the catheter for connecting theelectrodes to the data processor system 100.

FIGS. 5A and 5B illustrate cross-sectional views of two embodiments 20Aand 20B of a catheter such as catheter 20 shown in FIG. 4B. Eachembodiment has a lumen 60 for inflating and deflating the balloon and alumen 61 for suction and infusion. The sizes of these lumens can vary.The electrode leads 70A are embedded in the material of the catheter inthe embodiment shown in FIG. 5A, whereas the electrode leads 70B aretunneled through a lumen 71 formed within the body of catheter 20B shownin FIG. 5B.

Pressure conduits for perfusion manometry connect pressure ports 90, 91to transducers included in the data processor system 100. As shown inFIG. 5A, pressure conduits 95A may be formed in catheter 20A. In anotherembodiment, shown in FIG. 5B, pressure conduits 95B constituteindividual conduits within a tunnel 96 formed in catheter 20B. In theembodiments described above where miniature pressure transducers arecarried by the catheter, electrical conductors may be substituted forthese pressure conduits.

With reference to FIG. 6, in at least some embodiments, catheter 20connects to a data processor system 100, to a manual or automatic system105 for distension of the balloon, and to a system 106 for infusion offluid or suction of blood or other bodily fluid. The fluid for infusionmay be heated with heating unit 107 to between 37° C. and 39° C. or tobody temperature. The impedance planimetry system typically includes aconstant current unit, amplifiers, and signal conditioners, butvariations are possible. The pressure system typically includesamplifiers and signal conditioners. The system can optionally containsignal conditioning equipment for recording of fluid flow in the bodylumen.

In at least one embodiment, the system is pre-calibrated and a catheteris available in a package. The package also may contain sterile syringeswith fluids to be injected. The syringes are attached to the machine,and after heating of the fluid by the machine and placement of thecatheter in the body lumen of interest, the user presses a button thatinitiates the injection with subsequent computation of the desiredparameters. The CSA, parallel conductance, and/or other relevantmeasures, such as distensibility, tension, etc., will typically appearon the display panel in the PC module 160. The user can then treat theaortic aneurysm by placement of a stent.

If more than one CSA is measured at the same time, the system cancontain a multiplexer unit or a switch between CSA channels. In at leastone embodiment, each CSA measurement or pressure measurement will bethrough separate amplifier units.

In at least one embodiment, the impedance and pressure data are analogsignals which are converted by analog-to-digital converters 150 andtransmitted to a computer 160 for on-line display, on-line analysis, andstorage. In other embodiments, all data handling is done on an entirelyanalog basis.

The processor system includes software programs for analyzing theconductance data. Additional software calculates cross-sectional areasbased on a number of categories of data, as disclosed herein. However,as discussed in more detail below, to calculate for absolutecross-sectional values, certain errors must be reduced or eliminated.The software can be used to reduce the error in CSA values due toconductance of current in the lumen wall and surrounding tissue and todisplay the two-dimensional or three-dimensional geometry of the CSAdistribution along the length of the vessel (and, optionally, along withthe pressure gradient). In one embodiment of the software, a finiteelement approach or a finite difference approach is used to derive theCSA of organ stenosis, taking parameters such as conductivities of thefluid in the lumen and of the lumen wall and surrounding tissue intoconsideration.

In another embodiment, simpler circuits are used. As explained herein,absolute cross-sectional values may be calculated based on two or moreinjections of different NaCl solutions, which varies the conductivity offluid in the lumen. In other embodiments, the software contains the codefor reducing the error in luminal CSA measurement by analyzing signalsduring interventions, such as infusion of a fluid into the lumen or bychanging the amplitude or frequency of the current from the currentamplifier. The software chosen for a particular application may allowfor computation of the CSA with only a small error instantly or withinacceptable time during the medical procedure.

Referring now to FIG. 4A, catheter 22 measures conductance in the bodylumen by detecting the change in voltage between detection electrodes26, 28, as shown by the following equation:

$\begin{matrix}{{\Delta \; V} = \frac{I \cdot L}{C \cdot {CSA}}} & \left\lbrack {1\; a} \right\rbrack\end{matrix}$

Thus, the change in voltage, ΔV, is equal to the magnitude of thecurrent, I, multiplied by the distance between the detection electrodes,L, divided by the conductivity of the fluid in the lumen, C, and dividedby the cross-sectional area, CSA. Because the current (I), the distance(L), and the conductivity (C) normally can be regarded as calibrationconstants during a localization procedure, an inversely proportionalrelationship exists between the voltage difference and the CSA, as shownby the following equation:

$\begin{matrix}{{\Delta \; V} = \frac{1}{CSA}} & \left\lbrack {1b} \right\rbrack\end{matrix}$

In other words, as the cross-sectional area of the lumen decreases, thechange in voltage measured by catheter 22 increases. As discussedearlier, conductance and cross-sectional area are proportional. Thus,this equation permits the relative conductances or cross-sectional areasof various intralumen anatomical structures to be determined frommeasurement of the change in voltage across the lumen using at least oneexcitation electrode and one detection electrode.

This measurement, however, does not produce accurate, or absolute,values of conductance or CSA because the wall of the lumen andsurrounding tissue effectuate a loss of current. Further, when theimpedance electrode encounters a bifurcation, the measured conductanceover estimates the segment area. This error is related to the dimensionof the bifurcation and the angle of the branch, with an angle of 90°resulting in the largest error. As shown in FIG. 2B, the amplitude ofthe conductance is related to the size of the aortic branches; forexample, the conductance spike (increase in conductance) resulting fromthe thoracic branches is smaller than the conductance spike formed whenthe catheter is pulled past the abdominal branches. Although relying onthe relative conductances or CSAs is sufficient for the localization ofintraluminal structures, other embodiments for other purposes mayrequire the accurate determination of absolute values for CSAs.

At least some of the disclosed embodiments overcome the problemsassociated with determination of the size (cross-sectional area) ofluminal organs, such as, for example, in the coronary arteries, carotid,femoral, renal and iliac arteries, aorta, gastrointestinal tract,urethra, and ureter. In addition, at least some embodiments also providemethods for registration of acute changes in wall conductance, such as,for example, due to edema or acute damage to the tissue, and fordetection of muscle spasms/contractions.

The operation of catheter 20, shown in FIG. 4B, is as follows: forelectrodes 25, 26, 27, 28, conductance of current flow through the organlumen and organ wall and surrounding tissue is parallel; i.e.,

$\begin{matrix}{{G\left( {z,t} \right)} = {\frac{{{CSA}\left( {z,t} \right)} \cdot C_{b}}{L} + {G_{p}\left( {z,t} \right)}}} & \left\lbrack {2a} \right\rbrack\end{matrix}$

where G_(p)(z,t) is the effective conductance of the structure outsidethe bodily fluid (organ wall and surrounding tissue); C_(b) is thespecific electrical conductivity of the bodily fluid, which for bloodgenerally depends on the temperature, hematocrit, and orientation anddeformation of blood cells; and L is the distance between the detectionelectrodes. This equation shows that conductance, G(z,t), isproportional to the cross-sectional area, CSA (z,t). Thus, a largerconductance will reflect a larger cross-sectional area, and vice versa.

Equation [2a] can be rearranged to solve for cross-sectional areaCSA(z,t), with a correction factor, α, if the electric field isnon-homogeneous, as

$\begin{matrix}{{{CSA}\left( {z,t} \right)} = {\frac{L}{\alpha \; C_{b}}\left\lbrack {{G\left( {z,t} \right)} - {G_{p}\left( {z,t} \right)}} \right\rbrack}} & \left\lbrack {2b} \right\rbrack\end{matrix}$

where α would be equal to 1 if the field were completely homogeneous.The parallel conductance, G_(p), is an offset error that results fromcurrent leakage. G_(p) would equal 0 if all of the current were confinedto the blood and hence would correspond to the cylindrical model givenby Equation [1 a]. In one approach, finite element analysis is used toproperly design the spacing between detection and excitation electrodesrelative to the dimensions of the body lumen to provide a nearlyhomogenous field such that a can be considered equal to 1. Simulationsshow that a homogenous or substantially homogenous field is provided by(1) the placement of detection electrodes substantially equidistant fromthe excitation electrodes and (2) maintaining the distance between thedetection and excitation electrodes substantially comparable to the bodylumen diameter. In one approach, a homogeneous field is achieved bytaking steps (1) and/or (2) described above so that a equals 1 in theforegoing analysis.

G_(p) is a constant at any given position, z, along the long axis of abody lumen, and at any given time, t, in the cardiac cycle. Hence, twoinjections of different concentrations (and therefore conductivities) ofNaCl solution give rise to two equations:

C ₁ ·CSA(z,t)+L·G(z,t)=L·G ₁(z,t)  [3]

C ₂ ·CSA(z,t)+L·G _(p)(z,t)=L·G ₂(z,t)  [4]

which can be solved simultaneously for CSA and G_(p) as

$\begin{matrix}{{{CSA}\left( {z,t} \right)} = {L\frac{\left\lbrack {{G_{2}\left( {z,t} \right)} - {G_{1}\left( {z,t} \right)}} \right\rbrack}{\left\lbrack {C_{2} - C_{1}} \right\rbrack}}} & \lbrack 5\rbrack \\{{G_{p}\left( {z,t} \right)} = \frac{\left\lbrack {{C_{2} \cdot {G_{1}\left( {z,t} \right)}} - {C_{1} \cdot {G_{2}\left( {z,t} \right)}}} \right\rbrack}{\left\lbrack {C_{2} - C_{1}} \right\rbrack}} & \lbrack 6\rbrack\end{matrix}$

where subscript “1” and subscript “2” designate any two injections ofdifferent NaCl concentrations (and conductivities). For each injectionk, C_(k) gives rise to G_(k) which is measured as the ratio of the rootmean square of the current divided by the root mean square of thevoltage. The C_(k) is typically determined through in vitro calibrationfor the various NaCl concentrations. The concentration of NaCl used istypically on the order of 0.45% to 1.8%. The volume of NaCl solution istypically about 5 ml, but the amount of solution should be sufficient tomomentarily displace the entire local vascular blood volume or otherbody lumen fluid. The values of CSA(t) and G_(p)(t) can be determined atend-diastole or end-systole (i.e., the minimum and maximum values) orthe mean thereof. The value of CSA would vary through the cardiac cycle,but G_(p)(t) does not vary significantly.

Once the CSA and G_(p) of the body lumen are determined according to theabove embodiment, rearrangement of Equation [2a] allows the calculationof the specific electrical conductivity of bodily fluid in the presenceof fluid flow as

$\begin{matrix}{C_{b} = {\frac{L}{{CSA}\left( {z,t} \right)}\left\lbrack {{G\left( {z,t} \right)} - {G_{p}\left( {z,t} \right)}} \right.}} & \lbrack 7\rbrack\end{matrix}$

In this way, Equation [2b] can be used to calculate the CSA continuously(temporal variation, as for example through the cardiac cycle) in thepresence of bodily fluid.

In one approach, a pull or push through is used to reconstruct the bodylumen CSA along its length. During a long injection of solution (e.g.,10 s to 15 s), the catheter can be pulled back or pushed forward atconstant velocity U. Equation [2a] can be expressed as

$\begin{matrix}{{{CSA}\left( {{U \cdot t},t} \right)} = {\frac{L}{C_{b}}\left\lbrack {{G\left( {{U \cdot t},t} \right)} - {G_{p}\left( {{U \cdot t},t} \right)}} \right\rbrack}} & \lbrack 8\rbrack\end{matrix}$

where the axial position, z, is the product of catheter velocity, U, andtime, t; i.e., z=U·t.

For the two injections, denoted by subscript “1” and subscript “2”,respectively, different time points T₁, T₂, etc. may be considered suchthat Equation [8] can be written as

$\begin{matrix}{{{CSA}_{1}\left( {{U \cdot T_{1}},t} \right)} = {\frac{L}{C_{1}}\left\lbrack {{G_{1}\left( {{U \cdot T_{1}},t} \right)} - {G_{p\; 1}\left( {{U \cdot T_{1}},t} \right)}} \right\rbrack}} & \left\lbrack {9a} \right\rbrack \\{{{{CSA}_{1}\left( {{U \cdot T_{1}},t} \right)} = {\frac{L}{C_{2}}\left\lbrack {{G_{2}\left( {{U \cdot T_{1}},t} \right)} - {G_{p\; 1}\left( {{U \cdot T_{1}},t} \right)}} \right\rbrack}}{and}} & \left\lbrack {9\; b} \right\rbrack \\{{{CSA}_{2}\left( {{U \cdot T_{2}},t} \right)} = {\frac{L}{C_{1}}\left\lbrack {{G_{1}\left( {{U \cdot T_{2}},t} \right)} - {G_{p\; 2}\left( {{U \cdot T_{2}},t} \right)}} \right\rbrack}} & \left\lbrack {10a} \right\rbrack \\{{{CSA}_{2}\left( {{U \cdot T_{2}},t} \right)} = {\frac{L}{C_{2}}\left\lbrack {{G_{2}\left( {{U \cdot T_{2}},t} \right)} - {G_{p\; 2}\left( {{U \cdot T_{2}},t} \right)}} \right\rbrack}} & \left\lbrack {10b} \right\rbrack\end{matrix}$

and so on. Each set of Equations [9a], [9b] and [10a], [10b], etc., canbe solved for CSA₁, G_(p1) and CSA₂, G_(p2), respectively. Hence, onecan measure the CSA at various time intervals and therefore at differentpositions along the body lumen to reconstruct the length of the lumen.In at least one embodiment, the data on the CSA and parallel conductanceas a function of longitudinal position along the body lumen can beexported from an electronic spreadsheet, such as, for example, aMicrosoft Excel file, to diagramming software, such as AutoCAD®, wherethe software uses the coordinates to render a three-dimensionaldepiction of the lumen on the monitor.

For example, in one approach, the pull back reconstruction was madeduring a long injection where the catheter was pulled back at constantrate by hand. The catheter was marked along its length such that thepull back was made at 2 mm/sec. Hence, during a 10-second injection, thecatheter was pulled back about 2 cm. The data was continuously measuredand analyzed at every two second interval; i.e., at every 4 mm. Thus,six different measurements of CSA and G_(p) were taken which were usedto reconstruct the CSA and G_(p) along the length of the 2 cm segment.

In an additional embodiment, the wall thickness is determined from theparallel conductance for those body lumens that are surrounded by air ornon-conducting tissue. In such cases, the parallel conductance is equalto

$\begin{matrix}{G_{p} = \frac{{CSA}_{w} \cdot C_{w}}{L}} & \left\lbrack {11a} \right\rbrack\end{matrix}$

where CSA_(w) is the CSA of the lumen wall and C_(w) is the electricalconductivity of the wall. This equation can be solved for CSA_(w) as

$\begin{matrix}{{CSA}_{w} = \frac{G_{p} \cdot L}{C_{w}}} & \left\lbrack {11b} \right\rbrack\end{matrix}$

For a cylindrical body lumen, the wall thickness, h, can be expressed as

$\begin{matrix}{h = \frac{{CSA}_{w}}{\pi \; D}} & \lbrack 12\rbrack\end{matrix}$

where D is the diameter of the lumen, which can be determined from thecircular CSA(D=[4CSA/π]^(1/2)).

When the CSA, pressure, wall thickness, and flow data are determinedaccording to the embodiments outlined above, it is possible to computethe compliance (e.g., ΔCSA/ΔAP), tension (e.g., P*r, where P and r arethe intraluminal pressure and radius of a cylindrical lumen), stress(e.g., P*r/h, where h is the wall thickness of the cylindrical organ),strain (e.g., (C-C_(d))/C_(d) where C is the inner circumference andC_(d) is the circumference in diastole), and wall shear stress (e.g., 4μQ/r³ where μ, Q, and r are the fluid viscosity, flow rate, and radiusof the cylindrical lumen for a fully developed flow). These quantitiescan be used in assessing the mechanical characteristics of the system inhealth and disease.

In at least one approach for localization or measuring the conductance(and determining the cross-sectional area) of a body lumen, a catheteris introduced from an exteriorly accessible opening (for example, themouth, nose, or anus for GI applications, or the mouth or nose forairway applications) into the targeted body lumen. For cardiovascularapplications, the catheter can be inserted into the lumens in variousways, such as, for example, those used in conventional angioplasty. Inat least one embodiment, an 18 gauge needle is inserted into the femoralartery followed by an introducer. A guide wire is then inserted into theintroducer and advanced into the lumen of the femoral artery. A 4 or 5Fr. conductance catheter is then inserted into the femoral artery viawire, and the wire is subsequently retracted. The catheter tipcontaining the conductance electrodes can then be advanced to the regionof interest by use of x-ray (e.g., fluoroscopy). In another approach,this methodology is used on small to medium size vessels (e.g., femoral,coronary, carotid, iliac arteries).

In at least one example of a clinical application, obtaining an accuratemeasurement (within acceptable limits) of the luminal cross-sectionalarea of an aortic aneurysm enables accurate and scientific stent sizingand placement. Proper stent implantation improves clinical outcomes byavoiding under or over deployment and under or over sizing of a stent,which can cause acute closure or in-stent re-stenosis. In at least oneembodiment, an angioplasty or stent balloon includes impedanceelectrodes supported by the catheter in front of the balloon. Asdescribed herein, these electrodes enable the immediate, or real-timedetermination of the cross-sectional area of the vessel during theballoon advancement. This provides a direct measurement of non-stenosedarea and allows for the appropriate stent size to be selected. In oneapproach, impedance electrodes are located in the center of the balloonin order to deploy the stent to the desired cross-sectional area. Suchembodiments and procedures substantially improve the accuracy ofstenting and the outcome of such stenting, as well as reduce overallcosts.

In another embodiment, error due to the loss of current in the wall ofthe organ and surrounding tissue is corrected by injection of twosolutions of NaCl or other solutions with known conductivities. In oneapproach, a minimum of two injections with different concentrations ofNaCl (and, therefore, different conductivities) are required to solvefor the two unknowns, CSA and G_(p), However, in other embodimentsdisclosed herein, only relative values for conductance orcross-sectional area are necessary, so the injection of two solutions isnot necessary. In another approach, three injections will yield threesets of values for CSA and G_(p) (although not necessarily linearlyindependent), while four injections would yield six sets of values. Inone approach, at least two solutions (e.g., 0.5% and 1.5% NaClsolutions) are injected in the targeted vessel or other lumen. Studiesindicate that an infusion rate of approximately 1 ml/s for a five secondinterval is sufficient to displace the blood volume and results in alocal pressure increase of less than 10 mmHg in the coronary artery.This pressure change depends on the injection rate which should becomparable to the lumen flow rate.

In at least one approach, involving the application of Equations [5] and[6], the vessel is under identical or very similar conditions during thetwo injections. Hence, some variables, such as the infusion rate, bolustemperature, etc., are similar for the two injections. Typically, ashort time interval is to be allowed (1 to 2 minute period) between thetwo injections to permit the vessel to return to homeostatic state. Thiscan be determined from the baseline conductance as shown in FIG. 7A, 7B,8A, or 8B. The parallel conductance is preferably the same or verysimilar during the two injections. Dextran, albumin, or another largemolecular weight molecule may be added to the NaCl solutions to maintainthe colloid osmotic pressure of the solution to reduce or prevent fluidor ion exchange through the vessel wall.

In yet another embodiment, the NaCl solution is heated to bodytemperature prior to injection since the conductivity of current istemperature dependent. Alternatively, the injected bolus is at roomtemperature, but a mathematical temperature correction is made since theconductivity is related to temperature in a linear fashion.

In one approach, a sheath is inserted through either the femoral arteryor the carotid artery in the direction of flow. To access the loweranterior descending (“LAD”) artery, the sheath is inserted through theascending aorta. For the carotid artery, where the diameter is typicallyon the order of 5 mm to 5.5 mm, a catheter having a diameter of 1.9 mmcan be used, as determined from finite element analysis, discussedfurther below. For the femoral and coronary arteries, where the diameteris typically in the range from 3.5 mm to 4 mm, so a catheter of about0.8 mm diameter would be appropriate. The catheter can be inserted intothe femoral, carotid, or LAD artery through a sheath appropriate for theparticular treatment. Measurements for all three vessels can be madesimilarly.

At least one clinical application of the embodiments of the systems andmethods disclosed herein relates to the delivery of pacing leads used inCRT, and, in particular, the delivery of a coronary sinus lead. When CRTis employed, it is necessary to advance a lead into the coronary sinusand coronary veins branching therefrom in order to position theelectrode(s) adjacent to the left ventricle of the heart. Duringdelivery, the distal end of the coronary lead is advanced through thesuperior vena cava, the right atrium, the valve of the coronary sinus,the coronary sinus, and may be further advanced into a coronary veincommunicating with the coronary sinus, such as the great cardiac vein.Routing a lead along the desired path to implant the electrode in thedesired implantation site can be difficult. This is particularly truewith respect to steering leads through the coronary sinus and into abranching vein on the left myocardium (posterior lateral branch). Therelatively small diameter of the coronary veins of the heart, thevarious anomalies typical in vascular anatomy, and the number of branchveins associated with the anatomy make locating the desired pathchallenging. Using the catheters and systems disclosed herein, it ispossible to obtain precise measurements of the coronary sinus andrelated branching blood vessels, to facilitate the navigation of suchdifficult areas. In other words, the catheters and systems disclosedherein can obtain an accurate profile of the coronary venous system,including accurate identification of bifurcations along the length ofthe coronary sinus.

In at least one embodiment, a conductance catheter comprising a thinwire may be employed for delivering a lead into the coronary sinus or abifurcation branching therefrom. In this embodiment, the conductancewire can be pulled through the coronary sinus and used to create aconductance profile thereof. In this manner, a clinician can accuratelyidentify—with a high degree of specificity—the various bifurcationsbranching from the coronary sinus. The clinician can identify thebifurcation of interest and thereafter steer the conductance wiretherein. Once the wire is positioned within the bifurcation, the leadcan be inserted over the wire and placed within the desired bifurcation.This application can be conducted using the larger conductance cathetersdescribed herein as well; however, the relatively small diameter of aconductance catheter comprising a wire facilitates navigation throughthe narrow bifurcations branching from the coronary sinus.

Described herein are the protocol and results for one approach that aregenerally applicable to most arterial vessels. The conductance catheterwas inserted through the sheath for a particular vessel of interest. Abaseline reading of voltage was continuously recorded. Two containerscontaining 0.5% and 1.5% NaCl were placed in temperature bath andmaintained at 37° C. A 5 ml to 10 ml injection of 1.5% NaCl was madeover a 5 second interval. The detection voltage was continuouslyrecorded over a 10 second interval during the 5 second injection.Several minutes later, a similar volume of 1.5% NaCl solution wasinjected at a similar rate. The data was again recorded. Matlab® wasused to analyze the data including filtering with high pass and with lowcut off frequency (1200 Hz). The data was displayed using Matlab®, andthe mean of the voltage signal during the passage of each respectivesolution was recorded. The corresponding currents were also measured toyield the conductance (G=I/V). The conductivity of each solution wascalibrated with six different tubes of known CSA at body temperature. Amodel using Equation [1a] was fitted to the data to calculateconductivity C. The analysis was carried out with SPSS statisticalsoftware using the non-linear regression fit. Given C and G for each ofthe two injections, an Excel spreadsheet file was formatted to calculatethe CSA and GP as per equations [5] and [6], respectively. Thesemeasurements were repeated several times to determine thereproducibility of the technique. The reproducibility of the data waswithin 5%. Ultrasound was used to measure the diameter of the vesselsimultaneous with our conductance measurements. The detection electrodeswere visualized with ultrasound, and the diameter measurements was madeat the center of the detection electrodes. The maximum differencesbetween the conductance and ultrasound measurements were within 10%.

FIGS. 7A, 7B, 8A, and 8B illustrate voltage measurements in the bloodstream in the left carotid artery. Here, the data acquisition had asampling frequency of 75 KHz, with two channels—the current injected andthe detected voltage, respectively. The current injected has a frequencyof 5 KHz, so the voltage detected, modulated in amplitude by theimpedance changing through the bolus injection, will have a spectrum inthe vicinity of 5 KHz.

With reference to FIG. 7A there is shown a signal processed with a highpass filter with low cut off frequency (1200 Hz). The top and bottomportions 200, 202 show the peak-to-peak envelope detected voltage whichis displayed in FIG. 7B. The initial 7 seconds correspond to thebaseline; i.e., electrodes in the blood stream. The next 7 secondscorrespond to an injection of hyper-osmotic NaCl solution (1.5% NaCl).It can be seen that the voltage is decreased, implying increasedconductance (since the injected current is constant). Once the NaClsolution is washed out, the baseline is recovered as shown in FIGS. 7Aand 7B. FIGS. 8A and 8B show similar data corresponding to 0.5% NaClsolutions.

The voltage signals are ideal since the difference between the baselineand the injected solution is apparent and systematic. Furthermore, thepulsation of vessel diameter can be seen in the 0.5% and 1.5% NaClinjections (FIGS. 7A, 7B and 8A, 8B, respectively). This allowsdetermination of the variation of CSA throughout the cardiac cycle asoutline above.

The NaCl solution can be injected by hand or by using a mechanicalinjector to momentarily displace the entire volume of blood or bodilyfluid in the lumen segment of interest. For example, in a blood vessel,the pressure generated by the injection will not only displace the bloodin the antegrade direction (in the direction of blood flow) but also inthe retrograde direction (by momentarily pushing the blood backwards).In other visceral organs which may be normally collapsed, the NaClsolution will not displace blood as in the vessels but will merely openthe organs and create a flow of the fluid. In one approach, afterinjection of a first solution into the treatment or measurement site,sensors monitor and confirm baseline of conductance prior to injectionof a second solution into the treatment site.

The injections described above are preferably repeated at least once toreduce errors associated with the administration of the injections, suchas, for example, where the injection does not completely displace theblood or where there is significant mixing with blood. As previouslynoted, any bifurcation(s) (with branching angle near 90°) near thetargeted lumen can cause an overestimation of the calculated CSA,thereby resulting in a conductance spike (see FIG. 2B). Hence, generallythe catheter should be slightly retracted or advanced and themeasurement repeated. An additional application with multiple detectionelectrodes or a pull back or push forward during injection willaccomplish the same goal. Here, an array of detection electrodes can beused to minimize or eliminate errors that would result from bifurcationsor branching in the measurement or treatment site.

In at least one embodiment, conductance spikes when present can beeliminated or smoothed out through a number or computational processingmeans, including, without limitation, threshold limits, gradient,interpolation, and smoothing algorithms. Threshold limits can beprogrammed to ignore readings for points where the cross-sectional areais greater than a preset number. Threshold limits are convenient toprogram; however, using solely threshold limits will not allow fordifferentiation between bifurcations caused by luminal branches andthose caused by conditions such as aneurysms. Accordingly, considerationof the gradient (slope) where a conductance spike would correspond to alarge, or possibly infinite, gradient. This criterion can be used inconjunction with a smoothing algorithm (e.g., linear interpolation orcubic spline) to distinguish a bifurcation from a pathologicalcondition. Now referring to FIG. 2C, the data of FIG. 2B is shown afterthe conductance spikes have been eliminated using at least onecomputational processing means. Similar profiles can be generated forthe coronary sinus and, as such, the effective and convenient navigationthereof can be achieved. The width of the conductance spike (not shown)can represent the approximate size (or diameter) of the bifurcation.

In an alternative approach, error due to the eccentric position of theelectrode or other imaging device can be reduced by inflation of aballoon on the catheter. The inflation of the balloon during measurementwill place the electrodes or other imaging device in the center of thevessel away from the wall. In the case of impedance electrodes, theinflation of the balloon can be synchronized with the injection of abolus such that the balloon inflation would immediately precede thebolus injection. Our results, however, show that the error due tocatheter eccentricity is small.

The CSA predicted by Equation [5] corresponds to the area of the vesselor other lumen external to the catheter (i.e., CSA of vessel minus CSAof catheter). If the conductivity of the NaCl solutions is determined bycalibration from Equation [1a] with various tubes of known CSA, then thecalibration accounts for the dimension of the catheter and thecalculated CSA corresponds to that of the total vessel lumen. In atleast one embodiment, the calibration of the CSA measurement system willbe performed at 37° C. by applying 100 mmHg in a solid polyphenolenoxideblock with holes of known CSA ranging from 7.065 mm² (3 mm in diameter)to 1017 mm² (36 mm in diameter). However, if the conductivity of thesolutions is obtained from a conductivity meter independent of thecatheter, then the CSA of the catheter is generally added to the CSAcomputed from Equation [5] to give the total CSA of the vessel.

The signals are generally non-stationary, nonlinear, and stochastic. Todeal with non-stationary stochastic functions, one can use a number ofmethods, such as the Spectrogram, the Wavelet's analysis, theWigner-Ville distribution, the Evolutionary Spectrum, Modal analysis, orthe intrinsic model function (“IMF”) method. The mean or peak-to-peakvalues can be systematically determined by the aforementioned signalanalysis and used in Equation [5] to compute the CSA.

For the determination of conductance or cross-sectional area of a heartvalve, it is generally not feasible to displace the entire volume of theheart. Hence, the conductivity of the blood is transiently changed byinjection of a hypertonic NaCl solution into the pulmonary artery. Ifthe measured total conductance is plotted versus blood conductivity on agraph, the extrapolated conductance at zero conductivity corresponds tothe parallel conductance. In order to ensure that the two innerelectrodes are positioned in the plane of the valve annulus (2 mm to 3mm), in one embodiment, two pressure sensors 36 are placed immediatelyproximal and distal to (1 mm to 2 mm above and below, respectively) thedetection electrodes or sets of detection electrodes (see, e.g., FIGS.4A and 4F). The pressure readings will then indicate the position of thedetection electrode relative to the desired site of measurement (aorticvalve: aortic-ventricular pressure; mitral valve: leftventricular-atrial pressure; tricuspid valve: right atrial-ventricularpressure; pulmonary valve: right ventricular-pulmonary pressure). Theparallel conductance at the site of annulus is generally expected to besmall since the annulus consists primarily of collagen, which has lowelectrical conductivity. In another application, a pull back or pushforward through the heart chamber will show different conductance due tothe change in geometry and parallel conductance. This can be establishedfor normal patients, which can then be used to diagnose valvularstenosis.

In one approach, for the esophagus or the urethra, the procedures canconveniently be done by swallowing fluids of known conductivities intothe esophagus and infusion of fluids of known conductances into theurinary bladder followed by voiding the volume. In another approach,fluids can be swallowed or urine voided followed by measurement of thefluid conductivities from samples of the fluid. The latter method can beapplied to the ureter where a catheter can be advanced up into theureter and fluids can be injected from a proximal port on the probe(will also be applicable in the intestines) or urine production can beincreased and samples taken distal in the ureter during passage of thebolus or from the urinary bladder.

In one approach, concomitant with measuring the conductance,cross-sectional area, and/or pressure gradient at the treatment ormeasurement site, a mechanical stimulus is introduced by way ofinflating the balloon or by releasing a stent from the catheter, therebyfacilitating flow through the stenosed part of the lumen.

In another approach, concomitant with measuring the conductance,cross-sectional area, and/or pressure gradient at the treatment site,one or more pharmaceutical substances for diagnosis or treatment ofstenosis is injected into the treatment site. For example, in oneapproach, the injected substance can be a smooth muscle agonist orantagonist. In yet another approach, concomitant with measuring theconductance, cross-sectional area, and/or pressure gradient at thetreatment site, an inflating fluid is released into the treatment sitefor release of any stenosis or materials causing stenosis in the lumenor treatment site.

Again, it will be noted that the methods, systems, and cathetersdescribed herein can be applied to any body lumen or treatment site. Forexample, the methods, systems, and catheters described herein can beapplied to any one of the following hollow bodily systems: thecardiovascular system including the heart; the digestive system; therespiratory system; the reproductive system; and the urogenital tract.

Finite Element Analysis: In one preferred approach, finite elementanalysis (“FEA”) is used to verify the validity of Equations [5] and[6]. There are two major considerations for the model definition:geometry and electrical properties. The general equation governing theelectric scalar potential distribution, V, is given by Poisson'sequation as:

∇·(C∇V)=−1  [13]

where C, I and ∇ are the conductivity, the driving current density, andthe del operator, respectively. Femlab or any standard finite elementpackage can be used to compute the nodal voltages using Equation [13].Once V has been determined, the electric field can be obtained fromE=−∇V.

The FEA allows for the determination of the nature of the field and itsalteration in response to different electrode distances, distancesbetween driving electrodes, wall thicknesses, and wall conductivities.The percentage of total current in the lumen of the vessel (% I) can beused as an index of both leakage and field homogeneity. Hence, thevarious geometric and electrical material properties can be varied toobtain the optimum design, i.e. minimizing the non-homogeneity of thefield. Furthermore, the experimental procedure was simulated byinjection of the two solutions of NaCl to verify the accuracy ofEquation [5]. Finally, the effect of the presence of electrodes and thecatheter in the lumen of vessel was assessed. The error termsrepresenting the changes in measured conductance due to the attractionof the field to the electrodes and the repulsion of the field from theresistive catheter body were quantified.

Poisson's equation was solved for the potential field, which takes intoaccount the magnitude of the applied current, the location of thecurrent driving and detection electrodes, and the conductivities andgeometrical shapes in the model including the vessel wall andsurrounding tissue. This analysis suggests that the following conditionsare optimal for the cylindrical model: (1) the placement of detection(voltage sensing) electrodes equidistant from the excitation (currentdriving) electrodes; (2) the distance between the excitation electrodesshould be much greater than the distance between the detectionelectrodes; and (3) the distance between the detection and excitationelectrodes is comparable to the vessel diameter, or the diameter of thevessel is small relative to the distance between the driving electrodes.If these conditions are satisfied, the equipotential contours moreclosely resemble straight lines perpendicular to the axis of thecatheter and the voltage drop measured at the wall will be nearlyidentical to that at the center. Since the curvature of theequipotential contours is inversely related to the homogeneity of theelectric field, it is possible to optimize the design to minimize thecurvature of the field lines. Consequently, in one approach, one or moreof conditions (1)-(3) described above are met to increase the accuracyof the cylindrical model.

Theoretically, it is impossible to ensure a completely homogeneous fieldgiven the current leakage through the lumen wall into the surroundingtissue. It was found that the iso-potential line is not constant as onemoves out radially along the vessel as stipulated by the cylindricalmodel. FIGS. 11A and 11B show the detected voltage for a catheter with aradius of 0.55 mm for two different NaCl solutions (0.5% and 1.5%,respectively). The origin corresponds to the center of the catheter. Thefirst vertical line 220 represents the inner part of the electrode whichis wrapped around the catheter, and the second vertical line 221 is theouter part of the electrode in contact with the solution (diameter ofelectrode is approximately 0.25 mm). The six different curves, top tobottom, correspond to six different vessels with radii of 3.1 mm, 2.7mm, 2.3 mm, 1.9 mm, 1.5 mm, and 0.55 mm, respectively. It can be seenthat a “hill” 220, 221 occurs at the detection electrodes, followed by afairly uniform plateau in the vessel lumen, followed by an exponentialdecay into the surrounding tissue. Since the potential difference ismeasured at the detection electrode 220, 221, the simulation generatesthe “hill” whose value corresponds to the equivalent potential in thevessel as used in Equation [5]. Thus, for each catheter size, thedimension of the vessel was varied such that Equation [5] was exactlysatisfied. Consequently, the optimum catheter size for a given vesseldiameter was obtained such that the distributive model satisfies thelumped equations (Equations [5] and [6]). In this way, a relationshipbetween vessel diameter and catheter diameter can be generated such thatthe error in the CSA determination is less than 5%. In one embodiment,different diameter catheters are prepackaged and labeled for optimal usein certain size vessel. For example, for vessel dimensions in the rangeof 4 mm to 5 mm, 5 mm to 7 mm, or 7 mm to 10 mm, analysis shows thatoptimum diameter catheters will be in the range of 0.9 mm to 1.4 mm, 1.4mm to 2 mm, or 2 mm to 4.6 mm, respectively. The clinician can selectthe appropriate diameter catheter based on the estimated vessel diameterof interest. This decision will be made prior to the procedure and willserve to minimize the error in the determination of lumen CSA.

Thus, a number of the embodiments disclosed herein accurately calculatelumen cross-sectional area by measuring conductance and correcting forvarious errors inherent in such measurements. However, at least some ofthe disclosed embodiments provide for the localization of body lumenjunctions and other intraluminal anatomical structures using relativeconductances and/or cross-sectional areas. Because only relativedifferences in conductance or cross-sectional area are necessary foraccurate localization, the calculation of absolute values for variouslocations within the body lumen may be skipped in most instances.

Referring now to the embodiment shown in FIG. 9, one clinicalapplication of catheter 22 is shown. Specifically, catheter 22comprising stent 160 is positioned within an aorta 140 for the treatmentof an aortic aneurysm 145. As described above with respect to FIG. 4A, aset of excitation electrodes 25, 27, and detection electrodes 26, 28 arelocated on catheter 22, which is disposed within stent 160.

In this embodiment, catheter 22, and thereby stent 160, is introducedinto the blood stream percutaneously with a femoral approach. After thegraft is routed into the aorta, electrodes 25, 26, 27, 28 are activatedand electrical current flow is provided to the aortic lumen through thecatheter 22 as previously described herein. In one embodiment, prior toor concurrent with collecting the conductance data, the catheter 22 mayrelease fluid, such as a solution of NaCl having a known conductivity,into the aortic lumen, such that the fluid passing through the lumencomes into contact with the distal end of the electrodes 25, 26, 27, 28.

Conductance data is collected at a plurality of locations throughout theaorta 140 to determine a profile and cross-sectional area at variouspoints along the aortic lumen. Further, any inherent errors in collecteddata can be corrected using any of the computational processes disclosedherein. In this manner, precise cross-sectional values of the aorticlumen can be obtained, as well as an accurate profile map of the region.Based on that data, the aneurysm can be precisely located within theaorta (e.g., where a larger conductance value is detected), and thestent 160 may be properly sized to affix to the aortic wall bothdistally and proximally of the aneurysm.

Now referring to FIG. 10, a balloon 30 is used to distend stent 160within the aneurytic region of the aorta 140. Inflation of the balloon30 applies a force to the stent 160 which extends radially and pressesinto the vessel wall just above and just below the aneurysm. As notedwith respect to the embodiment shown in FIG. 9, the profile andcross-sectional area of the aorta determined from the conductance datacan be used to identify the optimal diameter to which the balloon 30should be inflated. Accordingly, the stent 160 can be accurately sizedto effectively treat the aneurysm. Furthermore, as the two necks of thegraft should be deployed on an atherosclerosis-free aorta, the profileand cross-sectional area of the aorta determined from the conductancedata can be used to identify a good landing zone for the deployment ofthe graft and thus prevent graft migration or endoleak.

While various embodiments of devices, systems, and methods forlocalization of body lumen junctures have been described in considerabledetail herein, the embodiments are merely offered by way of non-limitingexamples. Many variations and modifications of the embodiments describedherein will be apparent to one of ordinary skill in the art in light ofthe disclosure. It will therefore be understood by those skilled in theart that various changes and modifications may be made, and equivalentsmay be substituted for elements thereof, without departing from thescope of the disclosure. Indeed, this disclosure is not intended to beexhaustive or to limiting. The scope of the disclosure is to be definedby the appended claims, and by their equivalents.

Further, in describing representative embodiments, the disclosure mayhave presented a method and/or process as a particular sequence ofsteps. However, to the extent that the method or process does not relyon the particular order of steps set forth herein, the method or processshould not be limited to the particular sequence of steps described. Asone of ordinary skill in the art would appreciate, other sequences ofsteps may be possible. Therefore, the particular order of the stepsdisclosed herein should not be construed as limitations on the claims.In addition, the claims directed to a method and/or process should notbe limited to the performance of their steps in the order written, andone skilled in the art can readily appreciate that the sequences may bevaried and still remain within the spirit and scope of the presentdisclosure.

It is therefore intended that this description and the appended claimswill encompass, all modifications and changes apparent to those ofordinary skill in the art based on this disclosure.

1. A system for measuring a luminal cross-sectional area of a bloodvessel, the system comprising: a catheter having a proximal end and adistal end, the distal end of the catheter for placement into a bodylumen, the catheter comprising a first electrode and a second electrode,each of the first and second electrodes having a proximal end and adistal end, the distal ends of the first and second electrodes locatedbetween the proximal and distal ends of the catheter; and a processorconnected to the first and second electrodes of the catheter, theprocessor capable of collecting conductance data to determine a profileof the body lumen, the conductance data collected at a plurality oflocations within the body lumen and determined at each of the pluralityof locations when the distal ends of the first and second electrodes areimmersed in a fluid within the body lumen; wherein the processor furthercomprises a computational program capable of detecting a bifurcation inthe body lumen and distinguishing the bifurcation from a lesion.
 2. Thesystem of claim 1, wherein the processor is further capable ofcalculating a cross-sectional area of the body lumen at each of theplurality of locations within the body lumen using the conductance data.3. The system of claim 1, wherein the computational program is furthercapable of adjusting the conductance data to eliminate a conductancespike due to the detection of a bifurcation.
 4. The system of claim 1,wherein the catheter comprises a thin wire.
 5. The system of claim 1,wherein, the body lumen comprises an aortic lumen.
 6. The system ofclaim 1, wherein the body lumen comprises a lumen of a coronary artery.7. The system of claim 5, wherein the lesion comprises an aneurysm.
 8. Asystem for measuring a luminal cross-sectional area of a blood vessel,the system comprising: a catheter having a proximal end and a distalend, the distal end of the catheter for placement into a body lumen, thecatheter comprising a first electrode and a second electrode, each ofthe first and second electrodes having a proximal end and a distal end,the distal ends of the first and second electrodes located between theproximal and distal ends of the catheter, the catheter furthercomprising a passageway for passing fluid through the catheter to thelocation of the distal ends of the first and second electrodes, suchthat fluid passing through the passageway comes in contact with thedistal ends of the first and second electrodes; and a processorconnected to the first and second electrodes of the catheter, theprocessor capable of collecting conductance data to determine a profileof the body lumen, the conductance data collected at a plurality oflocations within the body lumen and determined at each of the pluralityof locations when the distal ends of the first and second electrodes areimmersed in a fluid within the body lumen, the processor further capableof calculating a cross-sectional area of the body lumen at each of theplurality of locations within the body lumen using the conductance data;wherein the processor further comprises a computational program capableof detecting a bifurcation in the body lumen and distinguishing thebifurcation from a lesion; wherein the fluid within the body lumencomprises a first fluid having a first conductivity and a second fluidhaving a second conductivity; and wherein the conductance data isdetermined at each of the plurality of locations when the distal ends ofthe first and second electrodes are immersed in each of the first fluidand the second fluid.
 9. The system of claim 1, wherein the catheterfurther comprises a third electrode and a fourth electrode, each of thethird and fourth electrodes having a proximal end and a distal end,wherein the first and third electrodes comprise excitation electrodesand the second and fourth electrodes comprise detection electrodes; andthe proximal ends of the third and fourth electrodes are connected tothe processor.
 10. The system of claim 9, wherein the fluid comprisesblood.
 11. The system of claim 8, wherein: the conductance datacomprises a first conductance value determined at each of the pluralityof locations when the distal ends of the first and second electrodes areimmersed in the first fluid and a second conductance value determined ateach of the plurality of locations when the distal ends of the first andsecond electrodes are immersed in the second fluid.
 12. The system ofclaim 11, wherein the profile of the body lumen is determined from thefirst and second conductance values collected from each of the pluralityof locations, the first conductivity of the first fluid, and the secondconductivity of the second fluid.
 13. The system of claim 1, wherein:the catheter further comprises a third electrode and a fourth electrode,each of the third and fourth electrodes having a proximal end and adistal end, wherein the first and third electrodes comprise excitationelectrodes and the second and fourth electrodes comprise detectionelectrodes; and the proximal ends of the third and fourth electrodes areconnected to the processor.
 14. The system of claim 13, wherein: thedistal ends of the first and third electrodes are located between theproximal and distal ends of the catheter and the distal ends of thesecond and fourth electrodes are located between the distal ends of thefirst and third electrodes.
 15. The system of claim 1, wherein thecomputational program comprises a smoothing algorithm.
 16. The system ofclaim 1, wherein the computational program comprises a gradient.
 17. Thesystem of claim 1, wherein the computational program comprises aninterpolation.
 18. The system of claim 1, wherein the computationalprogram comprises a threshold limit.
 19. The system of claim 15, whereinthe computational program further comprises a threshold limit. 20-67.(canceled)
 68. A system for measuring a luminal cross-sectional area ofa blood vessel, the system comprising: a catheter having a proximal endand a distal end, the distal end of the catheter for placement into abody lumen, the catheter comprising a first electrode and a secondelectrode, each of the first and second electrodes having a proximal endand a distal end, the distal ends of the first and second electrodeslocated between the proximal and distal ends of the catheter, thecatheter further comprising a passageway for passing fluid through thecatheter to the location of the distal ends of the first and secondelectrodes, such that fluid passing through the passageway comes incontact with the distal ends of the first and second electrodes; and aprocessor connected to the first and second electrodes of the catheter,the processor capable of collecting conductance data to determine aprofile of the body lumen, the conductance data collected at a pluralityof locations within the body lumen and determined at each of theplurality of locations when the distal ends of the first and secondelectrodes are immersed in a fluid within the body lumen, the processorfurther capable of calculating a cross-sectional area of the body lumenat each of the plurality of locations within the body lumen using theconductance data; wherein the processor further comprises acomputational program capable of detecting a bifurcation in the bodylumen and distinguishing the bifurcation from a lesion, thecomputational program further capable of adjusting the conductance datato eliminate a conductance spike due to the detection of a bifurcation;wherein the fluid within the body lumen comprises a first fluid having afirst conductivity and a second fluid having a second conductivity;wherein the conductance data is determined at each of the plurality oflocations when the distal ends of the first and second electrodes areimmersed in each of the first fluid and the second fluid, theconductance data comprising a first conductance value determined at eachof the plurality of locations when the distal ends of the first andsecond electrodes are immersed in the first fluid and a secondconductance value determined at each of the plurality of locations whenthe distal ends of the first and second electrodes are immersed in thesecond fluid; and wherein the profile of the body lumen is determinedfrom the first and second conductance values collected from each of theplurality of locations, the first conductivity of the first fluid, andthe second conductivity of the second fluid.